Photographic silver halide emulsions containing phytic acid



r 2,757,088 PHOTUGRAPHIC SILVER HALIDE EMULSIONS CGNTAINING PHYTIC ACID Gustave William Moessen, New Brunswick, N. J., assignor to E. 1. tin Font tie Nemonrs and Company, Wilmington, Deli, a corporation of Delaware No Drawing. Application December 30, 1953, Serial No. 401,381 8 Claims. (Ci. 957) This invention relates to photographic silver halide emulsions and more particularly to such emulsions which contain phytic acid or an alkali metal or ammonium salt thereof. Still more particularly, the invention relates to water-permeable colloid silver halide emulsions and emulsion layers containing phytic acid or an alkali metal or ammounium salt thereof and to their preparation. The invention also relates to photographic elements bearing such emulsion layers.

An object of this invention is to provide novel photographic silver halide emulsions or dispersions which have improved sensitivity and photolytic and delevolpment response. Another object is to produce such emulsions which have good speeds and low fogging properties. A still further object is to provide such emulsions which can be made by the ordinary technician with available economical chemical compounds. Still other objects will be apparent from the following description of the invention.

it has been discovered that photographic silver halide dispersions in water-permeable protective colloids having markedly improved sensitometric characteristics can be made by incorporating with such dispersions or emulsions a small amount of phytic acid or an alkali metal or ammounium salt thereof. A mixture of the acid and one or more of such salts or a mixture of two or more of the salts can be used.

The quantity of phytic acid and/or salts added to the emulsion will depend not only upon the particular phytic acid compound used but also upon the waterpermeable colloid and the nature of the silver halide grains. In general, from 0.00045 to 0.0060 mol of phytic acid compound per mol of silver in the silver halides provide adequate sensitometric characteristics, however, smaller or larger amounts may prove efiicacious in certain emulsion types.

The phytic acid compound can be added to the colloidsilver halide emulsion or dispersion at any stage in its preparation that is prior to the completion of the digestion period. Thus the phytic acid or a salt thereof may be added to the aqueous media during the silver halide precipitation step, during the ripening period, or prior to or during the initial stages of the digestion step but are preferably added just prior to, or during the early stages of, the digestion period. The aqueous emulsions or dispersions are then prepared for coating in any usual manner and coated onto a suitable film or paper sheet to form a light-sensitive layer.

Phytic acid (mesoinositol hexaphosphate) and its alkali metal salts, e. g., lithium, sodium and potassium salts and also the ammonium salts are known compounds and are commercially available. Phytic acid can be made from inositol, phosphoric acid and phosphorous pentoxide, but is usually obtained from natural sources, i. e., plant and animal. It has been represented by the formula:

HO O P 03H:

HzOaPOCH COPOsHz H 031 O OH H OP 03H:

HC OP OsHz tates Patent The salts are made by neutralization of the free acid with a base. Since phytic acid and its sodium salt are more soluble than the other salts the former are preferred.

The phytic acid compounds may be incorporated in emulsions containing any of the usual optical sensitizing dyes, e. g., cyanine, carbocyanine, merocyanine, pseudocyanine, kryptocyanine, hemicyam'ne, and cyazine dyes, and non-optical sensitizing agents, e. g., sulfur sensitizers, such as allyl thioureas, allyl thiocyanates, thiocyanates, compounds containing a silicon-hydrogen bond, sodium thiosulfate, and sodium hyposulfite, sensitizing metals and metal compounds, e. g., gold, palladium, mercury, iron, and thallium and their chlorides including mixtures of two, three or more of these.

The invention will be further illustrated, but is not intended to be limited by the following examples wherein the emulsion preparation and subsequent operations are carried out in the substantial absence of actinic light.

Example I A washed, undigested aqueous highly sensitive gelatino silver iodobromide emulsion was divided into three equal parts. To the first part there was added 0.00202 mol of phytic acid per mol of silver, to the second part was added 0.00202 mol of sodium hexametaphosphate per mol of silver, and no addition was made to the third part which served as a control. The pHs of all three portions were adjusted to a value of 6.3 with 3-normal NaOH and then they were digested, and the post-digestion operations were carried out in the usual manner with the addition of suitable hardening and anti-fogging agents. The finished flowable aqueous silver halide emulsions were coated onto a film base having an anchoring layer and dried in the usual manner. The relative speeds of the three coatings, as determined from the densities of the processed film strips, were found to be as given below:

To one portion of a washed gelatino silver iodobromide emulsion there was added a dilute aqueous solution of phytic acid in an amount of 0.00126 mol of phytic acid per mol of silver, to a second portion there was added a like amount of sodium phytate, a sodium salt of the phytic acidand the third portion was reserved as a control. The pH of the three portions was adjusted to 6.3 with 3 N NaOH and the emulsions were digested and the usual post digestion treatments were carried out in a conventional manner. The resulting coatings were tested as described in Example I, with the following results:

Emulsion Adjuvant Speed Fog Phytic acid 11.3 i4 Sodium phytate. 120 18 None 14 Example 111 ample I. The coated emulsions were tested and the sensitometric results were as follows:

Emulsion Adjuvant Speed Fog Phytic acid None Example IV Emulsion Adjuvant Speed Fog Phytic acitL 118 None 100 14 The invention is not limited to the preparation of colloid silver iodobromide emulsions as illustrated in the foregoing examples, but can be used in emulsions containing other simple or mixed silver halides, e. g., silver chloride, silver bromide, silver chlorobromide, silver chloroiodooromide, etc., emulsions.

Similarly, the invention is not limited to the use of elatin as the peptizing or dispersing or binding agent for the silver halide grains. Thus, various other waterpermeable or hydrophilic colloids, including those having reversible characteristics, can be substituted for all, or a portion of the gelatin. Suitable additional colloids include agar agar, polyglycuronic acid, zein, colloidon, water-soluble cellulose derivatives, e. g., hydrolyzed cellulose acetate, cellulose acetate, cellulose glycollate, cellulose acid phthalate and its alkali metal salts; polyvinyl alcohol, partially hydrolyzed poylvinyl esters and polyvinyl acetals including those containing color former nuclei, polyamides (water-permeable nylons), poly(1,3- dioxolanes), polymethacrylic caids and copolymers thereof with other vinyl compounds, e. g., styrene, isobutylene, acrylonitrile, etc., and other synthetic or natural resins and superpolymers having hydrophilic or water-permeable characteristics and which are capable of forming smooth, hard films.

The emulsions can, of course, be coated onto various types of film bases including cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cellulose proprionate, and cellulose nitrate and films made from superpolyrners, e. g., nylon, polyethylene terephthalate, polystyrene, polyvinyl chloride and copolymers thereof, e. g., poly(vinyl chloride or vinyl acetate), etc., paper and any of the usual sheet supports used for making photographic films and papers.

The photographicfilms bearing above emulsions which contain phytic acid or an alkali or ammonium salt of phytic acid can be used for various purposes including camera or portrait film, motion picture film, lithographic films, and X-ray film. The emulsions are especially use- 111 in medical X-ray films and provide stable, high-speed medical X-ray films which have high speeds and gammas and low fog values, even when stored for relatively long periods of time.

An advantage of this invention is that it provides simple and easily reproducible photographic silver halide emulsions which have good stability and adequate sen sitivity. Another advantage is that the emulsions do not require any special technique for their preparation. A further advantage is that the invention provides photographic silver halide emulsions which have good photolytic and development responses and they can be obtained in a simple manner. Still other advantages can be apparent from the above description.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows 1. A photographic emulsion comprising a dispersion of light-sensitive silver halide grains in a water-permeable protective colloid, said emulsion containing from 0.00045 mol to 0.0060 mol, per mol of silver, of a compound taken from the group consisting of phytic acid and its alkali metal and ammonium salts.

2. A photographic emulsion comprising a dispersion of light-sensitive silver halide grains in gelatin, said emulsion containing from 0.00045 mol to 0.0060 mol, per mol of silver, of a compound taken from the group consisting of phytic acid and its alkali metal and ammonium salts.

3. A photographic emulsion comprising a dispersion of light-sensitive silver halide grains in a water-permeable protective colloid, said emulsion containing from 0.00045 mol to 0.0060 mol, per mol of silver, of phytic acid.

4. A photographic emulsion comprising a dispersion of light-sensitive silver halide grains in a water-permeable protective colloid, said emulsion containing from 0.00045 mol to 0.0060 mol, per mol of silver, of sodium phytate.

5. A photographic emulsion comprising a dispersion of light-sensitive silver halide grains in gelatin, said emulsion containing from 0.00045 mol to 0.0060 mol, per mol of silver, of phytic acid.

6. A photographic emulsion comprising a dispersion of light-sensitive silver halide grains in gelatin, said emulsion containing from 0.00045 mol to 0.0060 mol, per mol of silver, of sodium phytate.

7. A photographic element comprising a film oasc bearing at least one layer of photographic emulsion of the type set forth in claim 1.

8. The process of making a photographic silver halide emulsion involving precipitation, washing and digestion operations, the step which comprises admixing with said emulsion, at some stage prior to the completion of the final digestion operation, from 0.00045 mol to 0.0060 mol, per mol of silver, of a compound taken from the group consisting of phytic acid and its alkali metal and ammonium salts.

References Cited in the file of this patent UNITED STATES PATENTS Sheppard Mar. 2, 1926 Sheppard July 6, 1926 OTHER REFERENCES 

1. A PHOTOGRAPHIC EMULSION COMPRISING A DISPERSION OF LIGHT-SENSITIVE SILVER HALIDE GRAINS IN A WATER-PERMEABLE PROTECTIVE COLLOID, SAID EMULSION CONTAINING FROM 0.00045 MOL TO 0.0060 MOL, PER MOL OF SILVER, OF A COMPOUND TAKEN FROM THE GROUP CONSISTING OF PHYTIC ACID AND ITS ALKALI METAL AND AMMONIUM SALTS. 